Detection of Norovirus in Saliva Samples from Acute Gastroenteritis Cases and Asymptomatic Subjects: Association with Age and Higher Shedding in Stool.

Eduard Anfruns-Estrada,Cristina Fuentes,Nuria Soldevila,Rosa Bartolomé,Thais Cornejo,Angela Dominguez,Lorena Coronas,Conchita Izquierdo,Efrén Razquin,Aurora Sabrià,Rosa Pintó,Sara Sabaté,Susana Guix,Nuria Torner,Albert Bosch

doi:10.3390/v12121369

Abstract

Norovirus infections are a leading cause of acute gastroenteritis outbreaks worldwide and across all age groups, with two main genogroups (GI and GII) infecting humans. The aim of our study was to investigate the occurrence of norovirus in saliva samples from individuals involved in outbreaks of acute gastroenteritis in closed and semiclosed institutions, and its relationship with the virus strain, virus shedding in stool, the occurrence of symptoms, age, and the secretor status of the individual. Epidemiological and clinical information was gathered from norovirus outbreaks occurring in Catalonia, Spain during 2017–2018, and stool and saliva samples were collected from affected and exposed resident individuals and workers. A total of 347 saliva specimens from 25 outbreaks were analyzed. Further, 84% of individuals also provided a paired stool sample. For GII infections, norovirus was detected in 17.9% of saliva samples from symptomatic cases and 5.2% of asymptomatic individuals. Positivity in saliva occurred in both secretors and nonsecretors. None of the individuals infected by norovirus GI was positive for the virus in saliva. Saliva positivity did not correlate with any of the studied symptoms but did correlate with age ≥ 65 years old. Individuals who were positive in saliva showed higher levels of virus shedding in stool. Mean viral load in positive saliva was 3.16 ± 1.08 log10 genome copies/mL, and the predominance of encapsidated genomes was confirmed by propidium monoazide (PMA)xx-viability RTqPCR assay. The detection of norovirus in saliva raises the possibility of oral-to-oral norovirus transmission during the symptomatic phase and, although to a lesser extent, even in cases of asymptomatic infections.

Highlights

Human noroviruses (HuNoV) are associated with 18% of diarrheal diseases worldwide and cause200,000 deaths among children every year, mostly in developing countries [1,2]
The percentage of symptomatic cases which were confirmed by detection of HuNoV in stool by RTqPCR was significantly higher in outbreaks associated with genogroup II (GII) strains than genogroup I (GI) strains (79.4% vs. 61.4%, p = 0.002)
We detected HuNoV RNA in 12.1% of studied cases and 3.6% of asymptomatic exposed subjects. This overall prevalence is slightly lower than data reported by Kirby et al [10], with differences being probably due in part to differences in the date of sample collection and to the fact that our study included cases infected by a higher diversity of genotypes

Summary

Introduction

Human noroviruses (HuNoV) are associated with 18% of diarrheal diseases worldwide and cause200,000 deaths among children every year, mostly in developing countries [1,2]. HuNoV are classified into 10 genogroups, with genogroup I (GI) and genogroup II (GII) being the most prevalent affecting humans, with more than 9 and 27 genotypes within GI and GII, respectively [6]. Individual differences in susceptibility to infections by different genotypes have been described depending on the expression of histoblood group antigens (HBGA), the expression of which is primarily determined by the FUT2 gene [7]. Secretor-negative individuals are resistant to several genotypes, infections in nonsecretors have been documented for GI., GI.3, GII., GII., GII., GII., GII., GII., and GII.17 [7,8,9]. HuNoV RNA has been detected by RTqPCR in saliva and the oral cavity of infected individuals with gastroenteritis, but the number of studies is very scarce. Kirby et al [10] detected 24% HuNoV

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